Hey all, anyone know when using any tuner that can adjust the tire size what are the downfalls of inputting the wrong tire size. For example if you are running 35" tires and input 30" tires your speedo will be out of course but will it hurt anything. Thanks.

 

if you dont mind me askin why would you want to do that????

 

biggest reason would be I use my gps for the speedo and the odometer would read incorrect I would register less miles than I actually put on, keep it on warranty longer. I have a 2008 f350 put on 37" tires from the stock ones and the speedo/odometer is out about 10%, it will just help in the long run.

 

It essentially has the same effect as lowering the axle ratio. For example, if you have 3.55 gears, and are running 35" tires but telling the computer it has 30" tires - the truck will perform as if you had about a 3.04 ratio (3.55 x 30 / 35) with the 30" tires.

Telling the computer the correct tire size will help it make some adjustments such as tranny shift points - but still are not going to overcome the physical realities.